Pressure applicator devices particularly useful for non-invasive detection of medical conditions

ABSTRACT

A probe for application to a body part particularly a finger of a patent to detect a change in the physical condition of the patient includes a housing defining a compartment closed at one end and open at the opposite end for receiving the distal end of the patient&#39;s finger and a medium wholly self-contained within the probe for applying a static pressure field substantially uniformly around the distal end of the patient&#39;s finger, of a predetermined magnitude sufficient to substantially prevent distention of the venous vasculature, uncontrolled venous backflow, and retrograde shockwave propagation into the distal end, and to partially unload the wall tension of, but not to occlude, the arteries in the distal end when at heart level or below. A sensor senses changes in the distal end of the patient&#39;s finger related to changes in arterial blood volume therein.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of application Ser. No. 10/073,342 filedFeb. 13, 2002 abandoned, which is a division of application Ser. No.09/485,302 filed Feb. 8, 2000 (now U.S. Pat. No. 6,461,305 issued Oct.8, 2002), which is a National Stage Application filed under 35 U.S.C.§371 of International Patent Application No. PCT/IL99/00292 filed Jun.2, 1999. The entire contents and disclosures of all of the precedingprior applications are incorporated herein by reference. TheInternational Application of which priority benefit is claimed waspublished under PCT Article 21(2) in English.

FIELD AND BACKGROUND OF THE INVENTION

The present invention relates to pressure applicator devices forapplying a predetermined static pressure to a body part of a patient.The invention is particularly useful as a probe for application to adigit (i.e., a finger or toe) of a patient for the non-invasivedetection of certain medical conditions in accordance with the methoddescribed in our PCT Application PCT/IL97/00249; and the invention istherefore described below especially with respect to such applications.

Our Application PCT/IL97/00249 (WO98/04182, published Feb. 5, 1998)discloses methods and apparatus for the non-invasive detection of achange in a physiological condition of a patient by monitoring changesin the peripheral arterial tone as manifested by changes in the arterialblood volume in a terminal extremity of a body part, preferably a digit(finger or toe) of the patient. The method and apparatus are describedin that application particularly for detecting mycardial ischemia andsleep apnea, and also for the continuous monitoring of blood pressure.The described apparatus includes a probe for application to thepatient's body part (e.g., finger) which probe includes a housing forreceiving the distal end of the patient's body part, and pressurizingmeans for applying a static pressure field substantially uniformlyaround the distal end of the patient's body part when received in thecompartment, including its terminal-most extremity. The static pressurefield is of a predetermined magnitude sufficient to substantiallyprevent distention of the venous vasculature, uncontrolled venousbackflow, and retrograde shockwave propagation into the distal end ofthe body part, and to partially unload the wall tension of, but not toocclude, the arteries in the distal end of the body part when at heartlevel or below. The probe further includes a sensor within the housingfor sensing changes in the distal end of the patient's body part relatedto changes in volume therein due to changes in instantaneous bloodvolume related to arterial tone.

That application described a number of probe constructions in which thestatic pressure field was applied via a remotely located pressure sourceconnected by tubing to a fluid chamber within the probe. However,utilizing such remotely-located pressure sources complicates theconstruction of the apparatus and also restricts the mobility of thepatient.

OBJECTS AND BRIEF SUMMARY OF THE PRESENT INVENTION

An object of the present invention is to provide a device particularlyuseful as a probe in the method and apparatus of the above-cited PCTApplication but of a simplified or improved construction as compared tothe devices described therein. Another object is to provide a probewhich does not restrict the mobility of the patient.

According to broad aspect of the present invention, there is provided adevice for application to a digit of a patient to detect a change in thephysical condition of the patient; the device comprising a probeincluding: a housing defining a compartment closed at one end and openat the opposite end for receiving the distal end of the patient's bodypart; pressurizing means for applying a static pressure fieldsubstantially uniformly around the distal end of the patient's bodypart, when received in the compartment, including the extreme distal tipof the patient's body part, which static pressure field is of apredetermined magnitude sufficient to substantially prevent distentionof the venous vasculature, uncontrolled venous backflow, and retrogradevenous shockwave propagation into the distal end, and to partiallyunload the wall tension of, but not to occlude, the arteries in thedistal end when at heart level or below; and a sensor for sensingchanges in the distal end of the patient's body part related to changesin volume thereof due to changes in instantaneous blood volume relatedto arterial blood volume therein; characterized in that the pressurizingmeans for applying the static pressure substantially uniformly aroundthe distal end of the patient's body part, including its terminal-mostextremity, is constituted of a medium wholly self-contained within theprobe.

A number of embodiments are described below for purposes of example.

According to further features in one class of embodiments describedbelow, the pressurizing means includes an inner resilient within thehousing and defining therewith an inner chamber to be filled with afluid for applying the static pressure via the membrane substantiallyuniformly around the distal end of the patient's body part, includingits terminal-most extremity.

According to further features in the latter described embodiments, thepressurizing means further includes an outer resilient membrane attachedto the housing externally thereof and defining therewith an outerchamber communicating with the inner chamber via openings in the housingfor enlarging the effective volume of the inner chamber such as to causethe inner membrane to apply substantially the same static pressurearound the distal end of the patient's body part despite changes involume therein.

A further embodiment is described below for purposes of example, whereinthe pressure means includes a body of resilient sponge material formedwith a recess defining the compartment for receiving the patient's bodypart when inserted therein.

The sensor within the housing is described below, for purposes ofexample, as being either an optical sensor for optically detecting, or aHall Effect sensor for magnetically detecting, volume changes in thesubject's finger which attend pulse-related blood volume changes andcorresponding finger girth changes.

As will be described more particularly below, the present inventionenables probes to be constructed with the static pressurizing meanswholly self-contained within the probe housing, thereby greatlysimplifying the construction of the probe as well as reducingrestrictions on the mobility of the patient using such a probe. However,the invention may also be implemented in a two-section probe wherein onesection includes a first housing attached to the body part and defininga part of the static pressurizing means, and the second section includesa second housing having another part of the static pressurizing means influid connection to the first section, the sensor being located withinthe second section.

While the invention is particularly useful in the methods and apparatusof the above-cited PCT Application, the invention, or various featuresthereof, can be used in other applications as will also be describedbelow.

Further features and advantages of the invention will be apparent fromthe description below.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is herein described, by way of example only, withreference to the accompanying drawings, wherein:

FIG. 1 is a longitudinal sectional view, and FIG. 1 a is a correspondingview but rotated 90° with respect to FIG. 1, illustrating one form offinger probe constructed in accordance with the present invention;

FIG. 2 is a graph of volume versus pressure, and

FIG. 3 is a graph of pressure versus time, both helpful in explainingthe operation of the finger probe of FIG. 1;

FIG. 4 is a view similar to that of FIG. 1, but omitting the sensor andillustrating a modification in the construction of the finger probe;

FIG. 5 is a view similar to that of FIG. 1, but illustrating anotherfinger probe constructed in accordance with the present invention;

FIGS. 6 a-6 c diagrammatically illustrate one manner of applying theprobe of FIG. 5 to a patient's finger;

FIGS. 7 a-7 c illustrate a modification in the construction of the probeof FIG. 5, and the manner of applying it to the patient's finger;

FIGS. 8 a-8 c diagrammatically illustrate another probe constructed inaccordance with the present invention;

FIG. 9 is a side elevational view diagrammatically illustrating a probesimilar to that of FIGS. 8 a-8 c but including another fasteningarrangement for fastening the two half-sections together;

FIGS. 10 a-10 c are views corresponding to FIGS. 8 a-8 c butillustrating another probe constructed in accordance with the presentinvention;

FIGS. 11 a-11 c illustrate another probe construction similar to that ofFIGS. 10 a-10 c;

FIG. 12 illustrates one manner of applying to a patient the probe ofFIGS. 11 a-11 c and a read-out to an electrical circuit;

FIGS. 13 a-13 c diagrammatically illustrate another probe constructionin accordance with the invention and showing particularly the elementsof the sensor and the manner of making electrical connections to them;

FIG. 14 illustrates a probe similar to that of FIG. 1 or 4 but includinga pressure cuff contiguous to the inner (proximal) end of the probe forextending the pressure field with respect to the sensor elements;

FIG. 15 illustrates another construction of a probe in accordance withanother aspect of the invention;

FIG. 15 a illustrates an overall apparatus including the probe of FIG.15;

FIGS. 16 and 16 a diagrammatically illustrate another probe constructionin accordance with the present invention;

FIG. 17 illustrates an overall apparatus including any of the otherdescribed probes; and

FIGS. 18 a-18 d diagrammatically illustrate a further probe constructionin accordance with the present invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

FIGS. 1 and 1 a illustrate one form of probe constructed in accordancewith the present invention particularly for use in the method andapparatus of the above-cited PCT Application for monitoring theperipheral arterial tone of a patient's body part (e.g., digit) in orderto indicate, in a non-invasive manner, the physiological state ormedical condition of the patient. As briefly described above, and asmore fully described in the above-cited PCT Application, such a probeincludes pressurizing means for applying a static pressure fieldsubstantially uniformly around the distal end of the patient's digit,including its terminal-most extremity (extreme distal tip), and a sensorfor sensing changes in the distal end of the patient's digit related tochanges in volume thereof due to changes in instantaneous blood volumerelated to arterial blood volume therein. The probe illustrated in FIG.1, however, is of a simplified construction as compared to the probesillustrated in the above-cited PCT Application, since the staticpressure means in the probe of FIG. 1 is constituted of a medium whollycontained within the probe.

The probe illustrated in FIGS. 1 and 1 a includes a housing 2 of rigidplastic material, closed at one end, and open at the opposite end, anddefining a compartment for receiving the patient's finger 3. An innermembrane 4 within housing 2 defines therewith a chamber 5 for receivinga fluid, such as air, which applies a static pressure fieldsubstantially uniformly around the distal end of the finger 3 includingits extreme distal tip. The probe illustrated in FIGS. 1 and 1 a furtherincludes a sensor constituted of one part 6 a on one side of the finger,and another part 6 b on the opposite side, for measuring changes involume of the patient's finger caused by arterial blood flow. Theillustrated probe further includes a U-shaped restraining bar 7 fixed byan annular ring 8 within the housing to cause the inner membrane 4 tomore firmly grip the patient's finger 3 when inserted into the probe.

The above-cited PCT Application is hereby incorporated by reference forfurther details of the construction of the probe and the manner of itsuse for monitoring a physiological state or medical condition of thepatient.

The probe illustrated in FIGS. 1 and 1 a, however, differs from thosedescribed in the above-cited PCT Patent Application in the manner ofproviding the substantially uniform static pressure applied around thedigital end of the patient's finger. Whereas in the examples illustratedin the above-cited PCT Application, such a static pressure is providedby a remotely-located pressure source coupled by tubing to the probe,the probe illustrated in FIGS. 1 and 1 a includes a static pressurizingmeans which is wholly self-contained within the probe housing.

For this purpose, the probe illustrated in FIGS. 1 and 1 a includes anouter resilient membrane 10 attached to the housing 2 externally thereofand defining with the housing an outer chamber 11. The outer membrane 10is of annular configuration and is applied around an annular portion ofthe housing spaced from its tip such that the outer chamber 11 is ofannular configuration. The outer annular chamber 11 communicates withthe inner chamber 5 by means of a plurality of openings 12 formedthrough housing 2.

The outer membrane 10 enlarges the effective volume of the inner chamber5 such as to cause, according to the Laplace Law, the inner membrane 4to apply substantially the same static pressure around the distal end ofthe patient's finger 3 despite changes in volume in chamber 5. Thus, theLaplace Law broadly states that the distending pressure (P) within adistensible hollow object is equal at equalibrium to the tension in thewall (T) divided by the two principal radii of curvature of the object(R1, R2); that is P=T (1/R1+1/R2). In a sphere, R1=R2; therefore P=2T/R.When the wall tension and the radius vary in direction proportion toeach other (i.e., T/R is constant), as is substantially the case forrubber balloons for most of the range above the minimum distention andbelow the maximum distention, the balloon distending pressure remainssubstantially constant irrespective of changes in volume.

FIG. 2 illustrates the relationship of pressure with respect to volumeand particularly shows the relatively large operating zone in which thepressure remains substantially constant with the changes in volume. Theactual pressure value is a function of the thickness and mechanicalcharacteristics of the distensible material.

The probe illustrated in FIGS. 1 and 1 a effectively enlarges the volumeof the inner chamber 5 by the volume of the outer chamber 11communicating with the inner chamber via openings 12 in the housing 2such that the static pressure applied by the fluid within chamber 5remains substantially constant irrespective of changes in volume ofchamber 5 caused by arterial blood flow within the patient's finger 3received within the probe. If the finger is partially removed fromwithin the probe, the remaining portion will still be subject to thesame external pressure because of the Laplace Effect.

The application of near diastolic counterpressures (40-70 mmHg), overthe entire surface of the distal phalanges of the finger, was found notto adversely affect tissue perfusion despite the knowledge thatlocalized pressure applied to tissues can cause collapse ofmicrocirculation. This is due to the fact that while arterial pressureexceeds the counterpressure permitting inflow of arterial blood, forblood to return via the veins venous pressure must overcome the appliedexternal pressure. The induced elevation of venous pressure causes theupstream microcirculation to be pressurized to a pressure levelintermediate between the outgoing venous blood and the incoming arterialblood; hence the transmural pressure of the microcirculation within theapplied pressure field is greater than zero and collapse of themicrocirculation is prevented.

The maintenance of fingertip surface temperature within a narrow rangearound 36° C., and the lack of a tendency for surface temperature tofall after 2 hours of 70 mmHg pressure application, supports the abovedescribed model of the preservation of microcirculatory patency andconsequently adequate tissue perfusion, as does the fact that overnightapplication of the pressurized probed on over 120 fingers in 60 subjectswas well tolerated with no deleterious effects.

In the probe illustrated in FIGS. 1 and 1 a, the inner chamber 5 isinitially filled with the fluid via a port 13 having a one-way valve 14permitting the fluid (e.g., air) to flow into the chamber, but not outof the chamber. FIG. 3 illustrates how the pressure varies with time,and shows that after a fixed quantity of air has been added, thepressure within the device remains relatively constant over a 24-hourperiod.

FIG. 4 illustrates a probe of the same construction as described abovewith respect to FIGS. 1 and 1 a, except that the sensor elements havebeen omitted for simplification purposes. Also, the port 13 and theone-way valve 14 have been omitted, and instead a fixed volume of fluidis permanently confined within the space defined by the internalmembrane 4 and the external membrane 10.

FIG. 5 illustrates a probe of similar construction as FIG. 4, exceptthat the outer membrane 20 is of tubular configuration to define anouter chamber 21 with the distal tip of housing 2. The outer chamber 21communicates with the inner chamber 5 via openings 22 formed in thehousing tip, so as to effectively enlarge the volume of the innerchamber 5 to produce the relatively constant static pressure applied tothe subject's finger 3 irrespective of changes in volume, as describedabove. Although FIG. 5 does not include the refill port or one-wayvalve, corresponding to elements 13 and 14 in FIGS. 1 and 1 a, theseelements could be included in which case they would be provided in theportion of housing 3 not covered by the outer membrane 21.

FIGS. 6 a-6 c illustrate one manner in which the probe constructed as inFIG. 5 may be manipulated to allow the patient's finger 3 to be insertedinto the probe. For this purpose, housing 2 of the probe is providedwith an annular ring 23 on the rigid portion of the housing spacedinwardly (proximally) from the outer membrane 20. A syringe including acylinder 24 and a plunger 25 is used for shifting the fluid from theinner chamber 5 to the outer chamber 21 in order to permit the patientto insert the finger into the probe. FIG. 6 a shows the open end ofcylinder 24 applied to ring 23; FIG. 6 b, shows the plunger 25 beingretracted within its cylinder 24, to thereby draw the fluid within theinner chamber 5 into the outer chamber 21, permitting the subject toinsert the finger into the probe, whereupon the plunger 25 may bereturned to its normal position within its cylinder 24; and FIG. 6 cshows the syringe being removed.

FIGS. 7 a-7 c illustrate another manner of manipulating the probe ofFIG. 5 to permit insertion of the subject's finger. This is done byproviding the outer membrane 20 with a finger piece including a knob 26externally of the membrane and fixed to a backing member 28 engageingthe inner surface of the membrane. Thus, knob 26 may be grasped by theuser and pulled outwardly (FIG. 7 b) to expand the outer chamber 21,thereby to draw into it the fluid from the inner chamber and to permitthe patient to insert the finger 3 into the probe. After the patient'sfinger has thus been inserted, knob 26 may be released, whereupon theprobe will assume the operative position illustrated in FIG. 7 c.

The function of the outer membrane 20 in the construction of FIGS. 7 a-7c is to facilitate the Laplace behavior as in the previously describeddesigns.

FIGS. 8 a-8 c diagrammatically illustrate a probe made of two sectionshinged together to enable the probe to be opened (FIG. 8 b) and closedaround the patient's finger (FIG. 8 c). Thus, as shown in FIG. 8 a, thehousing, generally designated 32, is also of tubular configurationclosed at one end and open at the opposite end for the insertion of thefinger 33. In this case, however, housing 32 is split into twohalf-sections 32 a, 32 b joined together along their length by anintegral hinge 32 c. Each housing section 32 a, 32 b includes an innermembrane strip 34 a, 34 b joined along the sides and end wall of therespective tubular section to define two internal chambers 35 a, 35 b.The probe further includes an outer membrane 36 a, 36 b for each housingsection 32 a, 32 b attached to the outer surface of the respectivehousing section to define the two outer chambers 37 a, 37 bcommunicating with the two inner chambers 35 a, 35 b via openings 38 inthe housing sections. The non-hinged sides of the two housing sectionscarry “Velcro” (T.M.) loop and hook fastener strips 39 a, 39 b, toenable the two sections to be tightly closed around the patient's finger33 to apply the desired pressure thereto.

FIG. 9 illustrates a two-section construction similar to that of FIGS. 8a-8 c, except that, instead of using “Velcro” (T.M.) fastener strips 39a, 39 b to fasten the two sections together, the fastening elements inthe construction illustrated in FIG. 9 include tongues 40 a receivedwithin slots 40 b integrally formed in the contacting edges of the twohousing sections 32 a, 32 b.

FIGS. 10 a-10 c illustrate another two-section probe construction, butin this case the two half-sections 42 a, 42 b are hinged together at theadjacent edges of the two end walls 43 a, 43 b of each housing section.In addition, instead of using an integral hinge, the hinge is in theform of a flexible non-extensible strip 44 bonded to the two end walls43 a, 43 b. The two half sections are secured in their closed conditionsby two “Velcro” (T.M.) strips 45 a, 45 b fixed to one of the housingsections 42 a at the open end of the housing and engageable with strips46 fixed to the other housing section 42 b. In all other respects, theconstruction of the probe illustrated in FIGS. 10 a-10 c issubstantially the same as described above and includes the outermembrane defining the outer chamber communicating with the inner chamberto provide the above-described Laplace behavior.

FIGS. 11 a-11 c and 12 illustrate a probe 50 mounted on the finger of ahand 51 (FIG. 12). Probe 50 is of the two-section construction as inFIGS. 10 a-10 c, and as more particularly illustrated in FIGS. 11 a-11c. The latter figures also illustrate the two-section inner membrane 53a, 53 b defining the two-section inner chamber 54 a, 54 b, and thetwo-section outer membrane 55 a, 55 b defining the two-section outerchamber 56 a, 56 b communicating with the inner chambers via openings57.

FIG. 11 a further illustrates the two sensor elements 58 a, 58 b fixedto the two inner membranes 53 a, 53 b, so as to be located at theopposite sides of the finger when received within the compartmentdefined by the probe, as shown in FIG. 11 b. The two sensor elements 58a, 58 b are connected by electrical conductors 59 to an electricalcircuit 60 (FIG. 12) fixed to a band 61, either directly connected, orby way of a glove. Electrical circuit 60, for example, could include thepower supply and other circuitry for driving the sensor elements 58 a,58 b, for receiving the outputs of those elements, and for storing theoutputs, e.g., in a storage device, so as to eliminate the need forexternal electrical connections when the device is being used.

FIG. 11 a further illustrates the provision of a pressure-sensitiveswitch P, or other pressure sensing device such as a strain gage, oninner membrane 53 b, to ensure that leakage has not occurred, and thatthe appropriate pressure has been reached, when the probe is applied tothe subject's finger. The pressure sensing device could be connected inseries with the optical sensor, or in parallel to the control device.

While many of the drawings, such as FIGS. 4, 7 a-7 c, 8 a-8 c, 9 and 10a-10 c, do not include the sensor elements corresponding to sensorelements 6 a, 6 b of FIGS. 1 and 1 a and sensor elements 58 a, 58 b ofFIGS. 11 a-11 c, it will be appreciated that these are omitted merelyfor purposes of simplifying the illustration and the description ofthese probes, and that such probes, when used for the particularapplications described above, would also include such sensor elements.As indicated earlier, the sensor elements in all the described examplescould be optical sensors, e.g., a light source (LED) and a lightreceiver for optically sensing the changes in the finger received withinthe probe; magnetic sensors, e.g., a permanent magnet and a magneticfield detector for sensing the changes in the finger girth by the HallEffect; or other types of sensors, such as described in the above-citedPCT Patent Application.

FIGS. 13 a-13 c illustrate one manner of mounting the sensor elements 58a, 58 b in the finger probe, and making the external electricalconnections to the sensor elements. Thus, each sensor element 58 a, 58 bis connected at one end to an electrical conductor 59 a, 59 b, having arubber plug 62 a, 62 b, at the opposite end, to provide airtight sealsin order to preserve the above described Laplace behavior. Plugs 62 a,62 b are receivable within openings 63 a, 63 b in the walls of the twohousing sections 52 a, 52 b hinged together by the strip 44 of flexiblenon-stretchable material. The two sensor elements 58 a, 58 b are fixedto the two diaphragms 53 a, 53 b within the compartment defined by thetwo housing sections 52 a, 52 b, such that when the sensor elements areassembled, and the two housing sections are in their closed condition asillustrated in FIG. 13 c, the two sensor elements engage the oppositesides of the finger received within the housing compartment. The sensorelements output signals, via the electrical conductors 59 a, 59 b whichpass through the housing wall, to the electrical processing and/orstorage system, such as the electrical circuit 60 (FIG. 12) on the band61 of the patient.

One of the plugs, e.g., plug 62 a, could be provided with the pressuresensing device P to ensure leakage does not occur, and that theappropriate level of pressure has been reached, when the probe isapplied, as described above with respect to FIG. 11 a.

FIG. 14 illustrates a finger probe having a thimble section 72 forreceiving the end of the patient's finger 73 and an annular pressurecuff 74 contiguous to the open end of the thimble section 72 on the sidenearer the heart of the patient when the probe is applied to thepatient's finger. Such a pressure cuff extends the static pressure fieldpast the sensor elements 58 a, 58 b towards the heart side of thepatient as described in the above-cited PCT Application. In this case,an inner diaphragm 75 is attached around its periphery to the innersurface of the thimble section 72 to define therewith an inner chamber76; and similarly, another inner diaphragm 77 is attached around itsperiphery to the inner surface of the annular cuff section 74 to definetherewith an inner annular chamber 78. In addition, an outer diaphragm79 is attached along one side of its periphery to the outer surface ofthe thimble section 72 and along the other side of its periphery to theouter surface of the annular section 74, to define with both sections acommon outer chamber 80. The outer chamber 80 communicates with innerchamber 76 via openings 81 in the thimble section 72, and with innerchamber 78 via openings 82 in the annular cuff section 74.

The sensor elements 58 a, 58 b are located within the thimble section72. This section applies the static pressure field described earliersubstantially uniformly around the distal end of the subject's finger73. This static pressure field is extended past the sensor elementstowards the heart side of the patient by the inner chamber 78 defined bymembrane 77 of the annular cuff section 74 as described in theabove-cited PCT Application. In this case, however, the common outerchamber 80 defined by the outer membrane 79 maintains substantially thesame static pressure field in both the thimble section 72 and theannular section 74 despite changes in volumes therein, according to theLaplace Law as described above.

In the above-described probes, the sensor elements (e.g., 6 a, 6 b inFIGS. 1 a, 1 b) are contained within the finger probe so as to belocated on opposite sides of the patient's finger when inserted into theprobe. In such arrangements, the sensor elements generate electricalsignals which are outputted via electrical conductors to processingand/or storage circuitry, e.g., electrical conductor 59 and storagecircuitry 60 in FIG. 12.

FIGS. 15 and 16 illustrate two arrangements wherein the sensor elementsare not located in the housing of the finger probe, but rather inanother housing separate from the finger probe and connected thereto byfluid tubes.

The probe illustrated in FIG. 15 is of the type illustrated in FIG. 14,including a thimble section 72 and an annular cuff section 74. The innerchamber 76 of the thimble section 72 is connected by a fluid tube 90 toa chamber 92 disposed within a second, rigid housing 93, which ispreferably mounted close to the finger probe, e.g., on the subjectswrist. Chamber 92 is defined by a cylinder 94 closed at one end by anend wall 95, and at the opposite end by a membrane 96.

Annular chamber 78 of the cuff section 74 is connected via another tube97 to another chamber 98 within the second housing 93. Chamber 98 isdefined by a cylinder 99 closed at one end 100 and at the opposite endby another membrane 101.

It will be seen that the two chambers 92 and 98 within the secondhousing 93 will be subject to the same pressures as chamber 76 in theprobe thimble section 72 and chamber 78 in the cuff section 74,respectively. These pressures will be opposed by the pressure within thesecond housing 93. The latter pressure may be preset by a syringe 102including a cylinder 103 coupled to the interior of housing 93, and aplunger 104 which is movable in order to change the volume, and therebythe pressure, within housing 93.

Chamber 92, connected via tube 90 to the thimble section 72 of theprobe, includes the sensor for sensing the volume changes within chamber76 of the thimble section 72, and thereby the physical condition of thepatient wearing the thimble. Thus, one sensor element 105 a is fixed tomembrane 96 so as to be displaced with that membrane, whereas the othersensor element 105 b is fixed to the bottom wall 95 of the chamber 92,such that sensor elements 105 a and 105 b together can be used tomeasure the volume changes within chamber 94.

Although, the FIG. 15 arrangement does not provide the advantage of thepreviously-described arrangements in having the pressurizing means, forapplying the static pressure substantially uniformly around the distalend of the patient's digit, to be constituted of a medium whollyself-contained within the finger probe, it does provide a number ofother advantages: Thus, the thimble section 72 of the probe in FIG. 15does not require an external chamber, as for example described withrespect to FIGS. 1 and 1 a, since chamber 94 within the second housing93, if vented to the atmosphere, would act as the external chamber toprovide the probe with the above-described Laplacian P/Vcharacteristics. Also, if the housing is not vented to the atmosphere,this arrangement enables convenient presetting of the pressures in boththe thimble section 72 of the probe, as well as in the annular cuffsection 74.

This arrangement also simplifies the construction of the probe attachedto the patient's finger since it locates the sensor elements in theseparate housing 93 rather than in the probe itself. Thus, the thimblesection of the probe could include two pliable plastic tubular elementseach closed at one end and open at the opposite end, and located in thethimble section so as to engage the opposite sides of the patient'sfinger when inserted therein, such that each such element definesone-half of the pressurizing-chamber. Also, the cuff section 74 could beomitted.

Another possible advantage in the FIG. 15 arrangement is that it tendsto avoid local bias towards smaller superficial blood vessels. Alsohousing 93 containing the sensor elements 105 a, 105 b, can be locatedvery close to the finger-applied probe, such as on a wrist band (FIG.12) to minimize the restrictions in the mobility of the patient and alsothe length of the fluid tubes 90, 97.

FIG. 15 a illustrates a variation in the construction of the apparatusof FIG. 15, in that the separate housing 93 includes a pressure sensor150 which senses the pressure within that housing and feeds thisinformation to a CPU 106. The CPU 106 also receives information from thepressure source 107 (e.g. the syringe 102 in FIG. 15) which presets thepressure within housing 93. The output signals from the sensor elements105 a, 105 b within housing 93, are also received by CPU 106 after theseoutputs have been amplified, filtered, and otherwise processed incircuit 108. The CPU 106 processes the foregoing inputs, e.g., asdescribed in the above-cited PCT Application, and produces an outputwhich is displayed in display 109.

In all other respects, the apparatus illustrated in FIG. 15 isconstructed and operates in the same manner as described above withrespect to FIG. 15, and therefore includes the same reference numeralsidentifying the corresponding parts.

FIGS. 16 and 16 a illustrate a finger probe of the same construction asdescribed above, particularly as illustrated in FIGS. 15 and 15 a, butincluding an adhesive layer to be contacted by the patient's fingerreceived within the finger probe. The adhesive layer is provided by adouble-sided adhesive strip 107, including an inner adhesive layer 107 aand an outer adhesive layer 107 b. The inner adhesive layer 107 a iscovered by a protective layer 108 which is stripped away, after thefinger has been inserted within the probe, to enable the inner adhesivelayer 107 a to contact and firmly adhere to the subject's finger whenreceived within the probe.

In all other respects, the probe illustrated in FIGS. 16 and 16 a may beof the same construction as described above, particularly with respectto FIGS. 15 and 15 a.

FIG. 17 illustrates apparatus including the novel finger probe used inapparatus, similar to that described in FIG. 23 of the above-cited PCTApplication, for effecting continuous non-invasive blood pressuremeasurements. For purposes of example, the finger probe illustrated inFIG. 17 is shown as being of the construction described above withrespect to FIGS. 11 a-11 c, although it will be appreciated that itcould be of any of the other described constructions.

Thus, the finger probe illustrated in FIG. 17 includes an electricalheater winding 110 applied around the outer surface of the probe housing52 a, 52 b for heating the patient's finger within the internal chamber54 a, 54 b of the probe to any predetermined temperature, preferably35-40° C. A thermister 111 or the like controls the electrical heater inorder to maintain that temperature so as to dilate the blood vessels inthe finger.

The probe illustrated in FIG. 17 further includes a vertical positionsensor 112 for sensing the vertical position of the finger probe withrespect to a reference point. Sensor 112 may be of the same constructionas described in the above-cited PCT Application, including a housingfilled with a liquid (preferably water) closed at one end by a flexiblemembrane 112 a and connected at its opposite end via a water filled tube113 to a pressure transducer 114. Transducer 114 produces an electricaloutput corresponding to the vertical position of sensor 112, and therebyof the finger probe, with respect to the subject's heart level.

The previously-described sensor elements 58 a, 58 b of the finger probeare connected via electrical conductors 115 to a circuit 115 a foramplifying and processing the output signals, and via an A/D converter116, to the CPU 117. The electrical heater winding 110 is supplied withpower via conductors 118 connected to an electrical power supply 119,also supplying power to the CPU 117. Thermister 111 is connected viaconductors 120 to a control circuit 121, which also produces an outputto the CPU 117 via the A/D converter 116. CPU 117 produces an output todisplay 122.

The manner in which the apparatus illustrated in FIG. 17 is calibrated,and then used, for the continuous non-invasive blood pressuremeasurements is described in the above-cited PCT Application.

FIGS. 18 a-18 d illustrate a further finger probe device including aself-contained pressurizing source eliminating the need for fluidconnections from the probe to an external source of pressurized fluid.In the probe illustrated in FIGS. 18 a-18 d, however, the pressurizingsource for applying the static pressure to the patient's finger is notprovided by a fluid chamber within the finger probe as in thepreviously-described embodiments, but rather is provided by a body ofresilient sponge material within the finger probe.

Thus, the finger probe illustrated in FIGS. 18 a-18 d includes a housing202 split into two half-sections 202 a, 202 b, hinged together along oneside by a flexible, non-extensible strip 203 and containing “Velcro”(T.M.) strips 204 at the opposite side for tightly clamping the probe tothe patient's finger 205 according to the static pressure to be applied.In this case, however, the means for applying the static pressure aroundthe patient's finger is in the form of a body of resilient spongematerial 206 a, 206 b, carried by each half-section of the probe. Alayer of a gel material 207 a, 207 b, covers the inner surface of eachof the sponge bodies 206 a, 206 b so as to be exposed for direct contactwith the patient's finger when inserted into the housing and the housingsections are in their closed condition as illustrated in FIGS. 18 c and18 d. The sensor elements 208 a, 208 b, which may be any of the devicesdescribed above, are carried on the inner surfaces of each of the spongebodies 206 a, 206 b, or their respective gel layers 207 a, 207 b.

It will be seen that any desired fixed pressure may be applied to thepatient's finger within the probe by applying the Velcro strips with theappropriate tightness to the two housing sections around the patient'sfinger. The gel layers 207 a, 207 b more securely fix the sponge bodiesand their sensor elements to the finger end, and more evenly dissipatethe applied force.

While the invention has been described with respect to several preferredembodiments, it will be appreciated that these are set forth merely forpurposes of example, and that many other variations may be made. Forexample, other sensors could be used than the optical and Hall-Effectsensors referred to above, e.g., as described in the above-cited PCTApplication. Other fasteners than the “Velcro” or other types describedabove could be used. Also, the probe may be incorporated in a glove tobe worn by the subject as also described in the PCT Application.

Further, the finger probe could be used to house a pulse oximeter formeasuring the oxygen saturation of blood. In such an application,conventional pulse-oximeter sensors could be included in the probehousing and would produce a better measurement of the oxygen saturationof the blood (SaO₂) because of the stable environment provided by thestatic pressure field.

It will be appreciated that all the embodiments described with respectto FIGS. 1-17 could be designed to provide the above-described Laplaceoperation, wherein the distending pressure remains substantiallyconstant substantially constant irrespective of changes in volume. Whilethe probe constructions of FIGS. 18 a-18 d, including the sponge cushionmaterial would not operate according to the Laplace law, it will beappreciated that a hybrid construction could be provided, wherein thesponge cushion is included to occupy only a part of the chambercontaining the sensors and thereby to provide substantially the Laplaceoperation.

In addition, the invention could be used in applications other thanfinger probes, e.g., as a supplement to a wound dressing for a bodypart, as a means for producing venous distention in a body part inprepartion for venapuncture, as a means for supporting, decompressingand/or immobilizing soft tissue injuries like sprains in a wrist orankle, as a pressure applicatior for edematous regions in a body part,and the like.

Another possible application of the invention is as a disposable sensor,based on a preinflated surface mounted membrane or membranes, capable ofbeing applied to a finger by being wrapped around the finger and havinga free end adhesively closed to impart uniform pressure to the enclosedmass of the finger. The membrane(s) may be mounted on an airtightbendable, but non-stretchable material such as plastic sheeting,rubberized cloth, or the like. A tube or tubes would communicate betweenthe finger probe and a sensing console which may be located at thewrist, for example. A unidirectional pressure release valve located atthe remote site would ensure that excess pressure is vented from thefinger probe upon its initial application.

A further possible application of the invention is in a verticaldisplacement sensor consisting of a single fluid filled tube connectedto an atmospheric pressure referenced pressure transducer at one end,and a compliant tip at the opposite end. The pressure transducer and thecompliant tip would be respectively situated at heart level and themeasurement site, or vice-versa.

A still further variation would be to provide the probe with thecombination of an optical sensor and a volumetric sensor within the sameprobe. The optical sensing elements need not be located on oppositesides of the finger as described, but could be at other locations. Oneparticularly useful arrangement is that in which optical sensor andlight source are respectively placed over the digital arteries, thusbeing oriented at about 140 degrees with respect to each other.

Many other variations, modifications and applications of the inventionwill be apparent.

1. A device to be applied around a body part of a patient, comprising aprobe including: a housing for application to the body part; andpressurizing means for applying a static pressure field substantiallyuniformly around the body part, said pressurizing means including: aninner resilient membrane within said housing and defining therewith aninner chamber to be filled with a fluid for applying said staticpressure via said membrane substantially uniformly around a distal endof the body part including a distal tip; and an outer resilient membraneattached to said housing externally thereof and defining therewith anouter chamber communicating with said inner chamber via openings in saidhousing enlarging an effective volume of said inner chamber such as tocause said inner membrane to apply substantially the same staticpressure around the body part despite changes in volume thereof.
 2. Thedevice according to claim 1, wherein the body part is a finger.
 3. Thedevice according to claim 2, wherein the inner resilient membrane isclosed at one end and open at an opposite end to define a compartmentfor receiving the finger.